Chemicomechanical process for making an unalterable white pigment



May 20 1924- DWORZAK CHEMICOMEGHANIGAL Pnocss Fon MAKING AN UNALTERABLEWHITE PIGMENT Filed May 26, 1919 E957* f2 aol? SfcoA/D FZ 001? ipigment.

Fatcnted May 20, 1924. i

UNITED lSTAT-as ADOLPH DWORZAK, 0F ST. LOUIS, MISSOURI.

CHEMICOMECHANICAL PROCESS FOR MAKING AN UNALTERABLE -WHITE PIG-KENT.

Application led Hay l26, 1919. Serial No. 299,873.

To all whom it may concern:

Be it known that I, ADoLrH Dwoaziui, a citizen of Russia, residing atthe city of St. Louis and State of Missouri, have in-v vented a new anduseful Chemicomechanica-l Process for Making an Unalterable WhitePigment, of which the following is a speciiication.

My invention relates to improvements in chemico-mechanical processes formaking au unalterable white pigment and 'my object is to provide simple,economical and uniform chemical treatment therefor and to provideapparatus for uniformly andy continuously and uniliterruptedlyperforming the several chemical steps, in a manner to continuouslyreceive and convey raw materials through' the treatment steps to acontinuous delivery of the finished product without manual assistance.

For my process I take common zinc blende which I convert into a purifiedsolution of zinc sulphate and I take common baryta rock which I convertinto a purified solution of barium sulphide and I then mix these twosolutions at a proper temperature and in equimolecular proportionthereby producing the double precipitate which forms my I then grind,Wash and otherwise physically refine my precipitate thereby making itsuitable for its intended use.

In my drawing I illustrate, in plan, three groups of mechanisms, whichgroups are by preference arranged one above another. as on' thefirst,lsecond and third floors. of a building, so that I may economize in thc`conveyance of substances from certain machines to subsequent machines.by gravity, and in my specification I employ numerals for designatingthe several mechanical treating means.

The zinc blende most suitablelfor my purpose is that containing about asixty per cent metalliccontent. This I grind on an ordinary differentialroll indicatedy by the numeral 5, on the drawing, and which is fed withthe zinc blendeby an ordinary conveyor designated A, the differentialroll being adjusted to deliver the mashed orc of such ineness as to letit pass a 40 to 60 mesh screen. The pulverized ore is next conveyed by achute B to a rotary roast-ing furnace 6 located by preference on thesecond floor, it being fed to the furnace 6'by a continuous feeder 7located at one end of the furnace. The rotary furnace 6 is heated byfuel, which is fed from the opposite end through a fuel feeder 8.

As the ore enters the furnace 6 it is ex posed to a graded'system oftemperatures which at the entry end of the furnace' is not to exceedl570F. As it progresses through the furnace by means of a screw conveyor, upto about three fourths of the furnace length it meets increasingtemperature until at the three fourths point it is exposed to atemperature of about 1170o F. the temperature within the furnacedecreases toward the discharge end where the temperature is not toexceed 660 F. The time during which the ore is treated is approximatelysix hours.` The purpose of this roasting step in the process is to driveofl' the sulphur, bismuth, antimony and any other volatile impurities. l

The thus roasted. andoxidized ore is gravity delivered from the furnace6, and at the delivery temperature, to an `enameled trough' 9.

At this point dilute sulphuric acid is added for the next step in myprocess. In order to make an acid solution of the proper strength Iprovide a lead linedtank 10 with an agitator 11 which tank has adelivery pipe 12 controlled by a valve 13. In this tank I prepare amixture of sulphuric acid and water, the condensate from certain orvarious of the heating coils employed in my process, to a specificdensity of 1.160. The trough 9 is equipped with a screw conveyor soarranged as to move the roasted ore, .for its delivery from the vtrough9 and at the same time thoroughly mix it with the acid solution. Thetrough 9 is provided with exteriorheating coils which maintain themixture of roasted ore and sulphuric acid at a temperature of about 300F.

The screw conveyor also is heavily enameled. to protect it from thecorrosive action of the sulphuric acid.

Thereafter From trough 9 by means of its screw conveyor the mixture ofore and acid is delivered to a series of oblong, closed topped treatmenttanks designated by numerals 14, 16 and 18, Each tank 14, 16 and 18 isprovided with a screw conveyor designated 15,

17 and 19 and both the interoir ofthe tanks as Well as all exposed partsof the screw conveyors are protected from corrosive action of the acideither by lead covering or by `heavy enameling.

When the mixture of roasted ore and sulphuric acid is delivered to thetank 14 there is a. certain amount of sedimentation and in order toconveniently handle both the sediment land supernatant liquor I makethese tanks of a novel shape lnamely that of a truncated substantiallysquare, pyramidv which I place with its major axis at an an le ofapproximately ten and three fourths egrees to the horizontal.

The action of the screw conveyor is that of moving the sediment upwardson the given degree toward the end of the truncated pyramidal tank fromwhich it is ejected into the larger end of an exactly similar tank 16with its conveyor 17. At this point I add fresh dilute sulphuric acidfrom tank 10. The delivery from tank 16 is to tank 18 in which anexactly similar step is conducted, but in which tank the last metalliczinc out of the treated (roasted) zinc ore, is separated by its treatingsolution, namely the dilute sulphuric acid.

The conveyor I19 of tank 18 delivers the treated ore to a sump pit 20where it is washed to recover any zinc left, with water, the condensatepreviously referred to, and the wash water removed by a pump 21 to tank14. f'

During the step of treatment in the tanks 14.-, 16 and l18 the dilutesulphuric acid converts .the lzinc content of the roasted ore intosoluble zinc sulphate which is carried along in solution. may obtain itis necessary that theconte'nt of these treatment tanks shall be heatedto boiling point and to this end the tanks are provided with lead coilsfed with steam.

The liquor containing the zinc as sulphate is pumped froml the thirdofthe serieso tanks 18 by a pump 22 to tank 23. In tank 23 the zincliquor is diluted with Water (oi condensation) and agita-ted until it isofv a speciic density of 1.380,. The sulphuric acid treatment as aboverecited yields a solution of the zinc blende and accordin `to theproportion of ore and acid this solution may or may not contain freeacid. Free acid is i objectionable to my process and if it be found hereit is at this point to be neutralized by the addition of more zincblende until a neutral solution is produced which neutral solution Icall my zinc liquor.

By' the above recited series of steps I have extracted from the zincblende all lof the available zinc and have adjusted the specific densityof its solution to a point best adapted to my process of makingunalterable white pigment and the sludge is drawn `oi at the ttom ofsaid tank to pit 20 from which it In order that this effectmaybediscarded orreturned to be retreated if its zinc content justifies.

The zinc liquor as thus prepared contains extraneous and objectionablecompounds, which as is well known to thosel versed in the art, cause bytheir chemical changes, reactions, 'or deteriorations, a degradationfrom pure white and itis therefore essential to the process of makingan'` unalterable White that these be elminated.' The zinc liquor in tank23 is therefore conducted from the top of the tank ytoan enameled orlead lined tank 24.

An intermediate step at this point is an electrolytic one, which takesplace in the electrolytic cells 23. The -purpose of the electrolysis isthat of the elimination of copper, and other bases of correspondingelectrolytic potential. Bases of the cop er po# tential class are firstelectrolytica ly deposited at relatively low volta eS, while such basesas cadmium may simi arly be electrolyticall deposited but, withincreased voltage, t 1e applicationrof lheat and as an adjunct agitationby heated air, all inthe presence of powdered zinc which is then addedin the tank 24 inv which there occurs a second electrolytic treatment.

The zinc liquor now freed from the above mentioned bases and held intank 24 is boiled by lead coils fed with steam and a itated 'by an 'airagitator which may be fe with hot air, or, should it be desirable tolower the temperature quickly, with cold air.

Much of the im urities thatV have been thrown down by e ectrolysis andthe zinc dust are held in suspension in the zinc liquor wherefore itbecomes necessary to remove them. The zinc liquor is therefore pum edfrom the tank 24 by a pump 27 to a fi ter 28, where the severalimpurities mentioned abeve are removed from the zinc liquor.

The step of boiling in the tank 24 by heated coils 25 and agitation byair agitator 26 and pumping by pump 27 and filtering by filters 28 istwice repeated by duplicate apparatus, including tank 30, withl itsheatin coil and agitator, pump 31. filter 32, an tank 33 with itsheating coil and agitator, pump 34 and filter 35..

In` tank 30 barium carbonate' is added in suiiicient quantity to reactwith, and precipitate any iron that may be present and electrolysis isapplied to precipitate any other lmpurities which may settle out 120,

ooI

'other in their rimpressed voltages, each voltage being appropriate toits particular electrolytic step and which actions are performed in thepresencefof an additional appropriate reagent.

The resulting liquor is then cooled with air and tested for neutralityand if found acid the acid condition is neutralized by the addition ofzinc oxide and .the foregoing neutralizing step is adjusted to give aneu,

tral solution at this step.

The liquor is now diluted with Water (the condensate) to adjust'itsspecicdensity to 1.283.

The liquor thus prepared consists primarily of zinc sulphate solutionafter passing through the filtration step 35 and is now suitable for thepreparation of my unalterable White pigment and is stored in tank 36 foruse later in the process.

i Concurrent with the preparation of the above described zinc sulphatesolution I prepare a barium sulphide solution. This solution is preparedby taking crude baryta rock, pulverizing it in an ordinary pulverizer37, to a neness corresponding to 100 mesh screen. Coal is likewisepulverized, the grade of coal being such as to contain not less than14000 B. t u.' per pound.

The baryta rock and the powdered coal are thoroughly mixed in a mixer38. The

proportion of ground baryta rock andground coal is approximately percent of thel former and 30 per cent of the latter which proportionalitydepends upon the barium content of the baryta and the sulphur content ofthe coal. This mixed powder is wetted with just suliicient water to forma paste and this paste is gravity fed to a long rotary furnace 39through which it travels continuously, this furnace-is in all respectssimilar to. furnace 6, used in the treatment of the zinc blende, but. inthe treatment of the baryta and coal mixture the maximum temperature isapproximately 1600o F. and exposed for a much shorter period, namely twoand one halfl hours.

By this step, the baryta rock is converted into barium sulphide which issoluble. The material thus treated is delivered from the furnace 39 to aheated trough 40. The Whole step herein recited being identical with theparallel step in the described zinc treatment.'

From the trough the baryta product is delivered to a series of threetruncated, square, pyramidal lixiviators similar in all respects totanks'14, 16 and 18 and their screw conveyors 15, 17 and 19, where thebarium sulphide is extracted, the nienstruum i being Water.

filter separates the barium sulphide held in solution from any sludgeGenerated by the ash content of the coal, wlliich sludge may have'beencarried along with the barium sulphide solution. barium sulphide fromvmost of the sludge it is passed through a tank, in lall respectssimilar to the tank 20, from which tank the pump 41 is fed. v

The barium sulphide liquor thusfreed from foreign insoluble matter t isfinally stored in tank 43 and this solution forms the companion solutionfor the zinc sulphate solution stored in tank 36. In order that thissolution ymay chemically fit the adjusted zinc sulphate solution it isdiluted with water (the condensate) to a specific density of 1.151. Thisbarium sulphide liquor being near the point of saturation and consequentcrystallization must be maintained at a temperature of at least 125 F. l

As has been previously stated this process consists in an equimolecularprecipitation between zinc sulphate solution of a specific density, bypreference 1.283 and a barium sulphide solution of specific density of,by preference, 1.151 andit may be determined by simple chemicalconsiderations that equimolecular balance is established when suchsolutions are mixed in the proportion of 1109' parts of the one to 1891parts of the other, respectively. y

In order to insure complete solubility of -these vreagents and to insuremost favorable chemical action between them I eli'ect this reaction atthe boiling point of the solutions and in order to further simplify myprocess I use thetanks 36 and 43 as. measuring tanks and they aretherefore of sizes corres onding to the proportionality above recite Ineffec-ting the mixture of these two solutions I first admit the properamount of zinc sulphate into -the mixing tank 45 and immediatelythereafter I admit the barium sulphide solutionto the same tank. It.being desirable to admit the barium sulphide solution quickly the tank43 is therefore provided with an adequately large delivery pipe., Iprovide tank 45 with an agitator 46 to insure very active agitation andin order to insure a complete double precipitation I continue to agitatothe mixture for no less than 15 minutes. The zinc sulfate and the bariumsullid react upon eachother in the well-known manner to form aprecipitate of zinc sulid and barium sulfate.

In order to free the At the completion 0f this reaction I pump themother liquid and its precipitate` by pumps 49 and 50, to a battery offilters 5l, 52, and A."i-l. The filtrate being conserved 1in anappropriate tank and the precipitate being conveyed to rotary dryer 57.My product is now in its highest state of purity for which reason theinterior of dryer 57 is enameled. This dryer is heated, either by wastegases from earlier steps in the process, or by steam, and maintained ata temperature of approximately 300'F.

Connected with dryer 57 is a suction fan 58 whose purpose. is to removethe Water vapor generatedI in the drying. In order that the dryingprocess may be continuons the interior of the dryer is provided with ahelical flight whereby the material in Athe act of drying is movedlongitudinally of the dryer and toward its discharge end. By thisspecific arrangement I avoid a continuous mixing of the thoroughlydriedprecipitate with moist precipitate. Theprecipitate, when thoroughlydried dumps out of the discharge end of the dryer directly into the bin59 and the communication between the dryer 57 and bin 59 is soconstructed that this last operation 'is out of contact with theatmosphere. Communicating with the bin 59 at the -bottom there isa drumprovided with only one opening which opening shall not exceed indimension one fifth of the drum circumference. This drum fitsaccurately, as may be: the. bottom of the bin and is air sealed to itagainst atmosphere. lVhen the drum'has been filled `with precipitate itis revolved so that the opening descends to a lowermost positiondischarging the precipitate into a second bin whereupon it is returnedto its former position to receive anew charge. l Contained within thelast mentioned bin is a pair of ribbed rolls through which theprecipitate in-its course of travel must pass. The purpose o't'theserolls is to crush the precipitate so that no particles ot' it shall belarger than of an inch,

After'the crushing,v the precipitate is delivered by gravity and out ofContact. with air to kiln 60 which is revoluble where the crushedprecipitate is reheated for calcination to a temperature of 1000o F. fora period of thirty minutes and any residual moisture -is driven oit,extracted and removedv by exhaust fan 58 (which keeps a certain vacuumin the furnace). all out of contact with the atmosphere. The exhaust fanproduces a partial vacuum in t'he'kiln 60, so that calcination proceedsunder a partial vacuum.'v lAfter the precipitate has4 been finallyldried and highly heated it is dumped from exit end -61 of kiln 60 intocold` water tank 62. The cold water quenching tank is so disposed thatany steam generated bv quenching the highly heated precipitate'may notenter the kiln 60 and4 also prevents contact with air'. y

In this last kiln (60) roasting any possible sulphur content in' theprecipitate is driven off and should therebe any other substances asidefrom the highly refractory y double precipitate this process ofcalcina-y tion volatilizes them.

When the pigment falls into the cold Water of the tank 62, shouldthereremain any refractory soluble matter it will vbe dissolved, and tosecure the thorough elimination of any such soluble' matter as well asto insure rapid' cooling this water is constantly renewed. The tank 62and the remaining tanks 63 and 64 of this series are in all respectssimilar to the truncated, square pyramidaltanks 14, 16 and 18, and thepigment served to these tanks is handled in a corresponding manner andfinally delivered to a sump'pit 65.

From the sump pit it is pumped by pum 66 to a battery of wet grindingmills 6 where it is ground to a tineness correspond-f ing to 200 mesh.From the delivery of the battery of the mills -67the pigment passes onto a rotary screen 68 Where a constant stream of Water is played on thegroundY pigment. returning the coarse material to pit whence it is againpumped to mill 67 to be reground.

The material of requisite tineness-which passes through the screen 68falls into a tank 69 and thence to a `series of tanks 70, similar to thetanks 14, 16 and 18. From this system of tanks 70 the liquid containingthe pigment runs into concrete pits 71 where the pigment is Washed'permitting the elimination of any alkaline salts or other foreignmatter.- The Washing in tanks 71 is by means of Water which isconstantly fed in from the bottom and this washing is assisted by airagitation.

This water bearing any soluble impuritiesflows away over the tops of thetanks.

The washing is continued till the Water shows no chemical reaction. 4Theigment is then collected in pit 72 from which it is removed by pump 73through pipe 74 to tank 75, which tank is oflarge diameter and providedwith a ho per bottom, this hopper bottom 'is provide with pi e 76 and avalve connected to pump 77 which delivers the pigment to the filter 78.The purpose ofthe tank 75 is to permit the sedimentation of the pigmentso that the pump 77 kand the filter 7 8V may handle a minimum of liquid.The pigment 'which is caught in filter 78 is conveyed by a pipe80 fromwhich the pigment is pressed into a dryer 81, similar to the dr er 57. i

From the ryer 81. the pigment is gravity fed to pulverizing mills 82which again pulverize the mate-rial to a fineness of a 200 mesh screen.

The reground pigment is delivered to a bin 83 either by a conveyor 'orblower fan 84, and the now finished for packing.

I claimy 1. The process which consists in causing to react upon eachother at substantially their. boiling temperature, a pureaqueoussolution of zlnc sulfate and a pure aqueous 1 lll pigment isready solution of barium sulfid, separating the resulting precipitatefrom the liquid, and drying the separated precipitate.

2. -The process which consists in causing a pure aqueous solution ofzinc sulfate to react upon a pure aqueous solution of barium suliid,separating the resulting precipitate from ythe liquid, drying suchseparated precipitate, crushing it, and then subjecting it tocalcination at a temperature higher than that used during theabove-mentioned drying operation.

3. The process which consists in causing solutions' of zinc sulfate 'andof barium sulfid to react upon each other, separating the resultingprecipitate from the liquid, drying such separated precipitate, crushingthe dried product and then subjecting it to a temperature higher thanthat used during the above-mentioned drying o eration, quenching the hotproduct, grin ing and Washing the quenched product, separating theliquid from the solids, and iinally drying Aand grinding such solids.

4. The process which conslsts in causing to react upon each other, a ureaqueous solution of zinc sulfate of a ensity of 1.283,

and a pure aqueous solution of barium sul- 5j The process which consistsin causing i to react upon each other at substantially their boilingtemperature, a pure aqueous solution of zinc sulfate of a densit of1.283 and a pure aqueous solution of barium suld ot a density of 1.151,separating the resulting precipitate from the liquid, drying theprecipitate at about 300 iF., crushing the dried precipitate and thenheating it for calcination, to about 1000 F. under exclusion of air,quenching the hot calcined product in cold liquid,.gr1nding and washingthe quenched product, separating the liquid from the solids, and finallydrying and grinding suchsolids.

6. The process which consists in causing to react upon each other,solutions of zinc sulfate and of barium sulfid, separating the resultingprecipitate from lthe liquid, drying the precipitate, crushing the driedprecipitate, and then calcining it under a partial vacuum.

l' ADOLPH DWORZAK.

